This invention relates to fluid spraying apparatus and more particularly to an improved, self-contained machine adapted to efficiently spray viscous sealing fluids, containing suspended solid material, onto an asphalt surface.
A good asphalt pavement seldom wears out but it is destroyed by external factors. As soon as a freshly laid hot mix pavement begins to cool it also begins an aging process which will eventually destroy the asphaltic binder and reduce the pavement to a layer of loose stone. The binder undergoes chemical reactions with the oxygen in the air and water or other liquids on the surface. At first this process is necessary for the pavement to become hard and firm but if the process is not arrested complete deterioration of the binder can take place. Sealing the pavement after the curing period can protect the asphalt from these destructive forces and can provide even a weak pavement with a much longer useful life.
There are several types of sealing agents and several methods used to seal asphaltic pavement. Two of such agents which are widely used in sealing and finishing asphalt surfaces such as parking lots, drive ways, and the like, are Asphalt Emulsions and Coal-tar-pitch emulsions. Two common methods used to apply these agents are either squeeging the fluid over the surface or spraying the fluid onto the surface. Each combination of method and agent has its own particular advantages and disadvantages.
For example, spraying machines are simple to maintain and easy to use but most require that the fluid be free of solids and diluted considerably for proper spray characteristics.
Squeeging machines can apply undiluted sealant containing sand or other solid fillers but have a high initial cost and require a high degree of maintenance because of the severe wear of the spreading and brushing components.
Asphalt emulsion type sealing material is generally made up of an asphalt emulsion, fine silica sand, and sometimes other selected fillers such as asbestos. This type of sealing is used where low cost is necessary. However, they are not resistant to oil, gasoline, or other petroleum fuels. They do fill small voids in asphalt pavement and form a relatively smooth but skid resistant surface which protects the subsurface from harmful effects of sun, water, and frost. They are applied by a hand squeegee or mechanical squeegeing means well known in the art. One example of a suitable mechanical squeegee type machine is the Seal-Mor model SM-175, manufactured by Neal Mfg. Co. of Villa Rica, Ga., which can apply the same amount of material as 8 or 10 men could using hand squeegees or about 150,000 sq. ft. per day. Another of this type is disclosed in U.S. Pat. No. 3,279,337.
Coal-tar-pitch sealing is a more widely accepted material for sealing bituminous pavements because it seals in the natural asphalt oils while preventing damage by oils, gasoline and most other petroleum fuels while also protecting against the harmful effects of sunlight, rain, and road salts. The composition of coal-tar pitch emulsions is exemplified by Federal Specification R-P-335d which indicates that a typical sample should contain at least 47% nonvolatile organics and up to 54% water so as to yield a specific gravity of at least 1.20. Usually the emulsion must be diluted with additional water, from 7 to 20% prior to use so that the material may be applied in a uniform thin coating onto the asphalt pavement.
Similar spraying machines have been developed, for example the type disclosed in U.S. Pat. No. 962,728 or 3,858,761, but are of limited use commercially because of numerous disadvantages. Usually the prior art provides a tank and a spray means coupled by a gear-type, positive displacement pump which provides fluid at a high flow rate and sufficient pressure only when the fluid is diluted so as to have a relatively low viscosity. Typically sealants are diluted 50% or more with water. This high amount of dilution renders prior art spraying machines less efficient than the squeegee-type machines which typically can apply an emulsion diluted with only 10 to 20 percent water.
Another disadvantage with prior art spraying machines is their inability to apply fillers such as sand along with the sealer. It is necessary to spray the sealer onto the pavement then apply the sand separately, usually by hand, which results in non-uniform coverage.